Optical properties of trivalent samarium-doped Ba5Zn4Y8O21 nanodiametric rods excitable by NUV light

A series of reddish-orange Ba5Zn4Y8-xO21:xSm(3+) (x = 0.04-0.24) nanophosphors were synthesized via urea-assisted solution combustion method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance (DR) and photoluminescence (PL) spectroscopy. Rietveld analysis infers that Y3+ ions can be well-substituted by Sm3+ ions without any major alteration in the crystal structure of host matrix. Moreover, as no JCPDS data was available for the host, the lattice parameters and refined atomic positions were determined for both, the host as well as the doped sample. TEM investigation revealed the nanodiametric rods of almost smoothly-surfaced morphological character. The optical band-gap of the host (5.36 eV) was calculated from DR spectra and also performed theoretically in density functional theory (DFT) framework using CASTEP code. On NUV excitation, the nanophosphor exhibits the characteristic emission peaks of Sm3+, which can be credited to (4)G(5/2) -> 6(Hj) (J - 5/2, 7/2, 9/2,11/2) transitions. The optimum Sm3+ concentration for better luminescence was found to be 1.5 mol%. The critical distance (20.49 angstrom) elicits the right mechanism responsible for concentration quenching (dipole-dipole). The detailed analysis of PL decay curves gave the radiative lifetime (1.11 ms), overall rate of non-radiative relaxation (240.16 s(-1)) and most importantly, the quantum efficiency of (4)G(5/2) 2 electronic state (78%). The CIE color coordinates unveiled an almost pure reddish-orange emitter, which finds potential applications in phosphor-converted white light emitting diodes (PC-WLED5) under NUV excitation. (C) 2018 Elsevier B.V. All rights reserved.